This invention relates generally to the field of devices for cardiac surgery, and more specifically to devices for R-F ablation of cardiac tissue.
The present invention is directed toward treatment of tachyarrhythmias, which are heart rhythms in which an chamber or chambers of the heart exhibit an excessively fast rhythm. In particular, the present invention is directed toward treatment of atrial arrhythmias which result from the presence of macro and/or micro-reentrant wavelets (e.g. atrial flutter and atrial fibrillation) and treatment of ventricular tachycardia.
Therapies have been developed for treating tachycardias by destroying cardiac tissue containing identified ectopic foci or aberrant conduction pathways. A variety of approaches have been taken, including application of electrical energy or other forms of energy to destroy the undesired cardiac tissue. As examples, ablation of cardiac tissue has been accomplished by means of radio frequency electrical current, direct current, microwave energy, heat, electrical pulses, cryothermy, and lasers. At present, ablation using R-F energy is perhaps the most widely practiced in the context of ablation procedures that can be carried out by means of a catheter, inserted into the closed heart.
Most R-F ablation catheters employ electrodes which are intended to contact the endocardium of the heart, or, as in U.S. Pat. No. 5,083,565, are intended to penetrate the endocardium and enter the myocardium. In general, R-F ablation catheters are effective to induce small lesions in heart tissue including the endocardium and inner layers of myocardium, in the immediate vicinity of the electrode. However, the medical community has expressed a desire for devices which produce larger and/or longer lesions, to reduce the number of applications of energy (burns) required to effectively ablate cardiac tissue associated with more complex arrhythmias such as atrial flutter or atrial fibrillation and ventricular tachycardia.
R-F ablation causes tissue in contact with the electrode to heat through resistance of the tissue to the induced electrical current therethrough. The actual extent of heating is somewhat unpredictable. However, temperature tends to rise as the duration and amplitude of the R-F signal increase. Heating of the tissue beyond a certain point can cause dissection or charring of the tissue, resulting in a high impedance between the R-F electrode and the return electrode, which in turn leads to cessation of the heating process, and, in some cases, causes the electrode to stick to the charred tissue. One response to this phenomenon has been the inclusion of thermocouple within the ablation electrode, in conjunction with feedback control to modulate the R-F signal to maintain the electrode temperature at a set parameter. One such system is disclosed in U.S. Pat. No. 5,122,137.
Particularly in the context of treating macro and/or micro-reentrant atrial arrhythmias, it has been proposed to create elongated lesions, to define a line of tissue which blocks the passage of depolarization wavefronts. This has, in some cases been accomplished by means of a series of small, individual lesions, each produced by a separate application of R-F energy. As disclosed in U.S. patent application Ser. No. 08/302,304 by Mulier et al, for a xe2x80x9cMethod and Apparatus for R-F Ablationxe2x80x9d, it has been proposed that an elongated, coil electrode might instead be employed to produce an elongated lesion with a single application of R-F energy. An elongated coil ablation electrode is also disclosed in published PCT application No. WO94/11059 for a xe2x80x9cFluid Cooled Ablation Catheter, by Nardella.
The present invention is directed toward expanding and improving the clinical applicability of R-F ablation, by accurately determining the ablation site and by increasing the overall size and extent of the lesions induced by R-F ablation. These goals are pursued by means of an ablation catheter employing one or more electrodes extending of substantial length, located adjacent the distal end of the catheter, in conjunction with a temperature control system employing multiple temperature sensors, arranged along the electrode or electrodes.
In one preferred embodiment, the electrode or electrodes extend over a distal segment of the catheter body, and multiple thermocouples or other temperature sensors are provided along the distal segment. The thermocouples may be used to individually regulate the power applied to individual electrodes along the distal segment. Alternatively, the temperature sensors may be used together to regulate the power applied to the electrode or electrodes, for example by employing the highest measured temperature to control the power applied to one or more electrodes.
In another preferred embodiment, the catheter may be provided with a mechanism for deflecting the distal segment of the catheter body, to provide directional control to the catheter, facilitating placement of its ablation electrode or electrodes at a desired location in the heart, and in close contact with heart tissue. Deflection may be accomplished, for example, by means of internal control wires which induce a curvature in the catheter body when displaced longitudinally. Alternatively, the distal portion of the catheter body may be preformed to display a curved configuration, and may be delivered through a guide catheter. In this case, the distal portion of the catheter body displays its preformed curve as it is advance out the distal end of the guide catheter. In a another preferred embodiment, the catheter body may display a generally straight configuration, with the distal portion located in the heart by means of a deflectable guide catheter, which may provided with internal control wires which allow the distal end of the guide catheter to be deflected.
The features of the embodiments discussed above may also be provided in catheters provided with mapping electrodes, allowing for mapping and ablation to be performed with the same catheter. Similarly, the features of the above described embodiments may also be combined with one another, if desired.